The present invention relates generally to gas turbine engines, and, more specifically, to variable stator compressor vanes.
A typical gas turbine engine compressor includes several rows or stages of compressor stator vanes and corresponding rows or stages of compressor rotor blades therebetween. During operation, air is sequentially compressed in the compressor stages and channeled to a combustor for being mixed with fuel and ignited for generating hot combustion gases which power the engine.
Compressor performance is improved by providing variable stator vanes which are selectively rotated about their longitudinal or radial axes. This is accomplished by attaching a corresponding lever arm to the radially outer ends of the vanes and joining the several levers to a common actuation or unison ring for providing uniform adjustment of the individual vanes to maximize compressor performance.
Each of the variable vanes must be identically angled relative to the other vanes in the row to maximize efficiency and prevent undesirable aerodynamic distortion from a misaligned stator vane.
In order to ensure proper alignment of the individual stator vanes, each vane typically includes a generally D-shaped seat around which a complementary D-shaped mounting hole of the lever is positioned. A threaded stem extends from the seat and receives a nut which secures the individual levers to the corresponding vanes.
The lever mounting holes and corresponding vane seats are typically sized with close manufacturing tolerances to ensure accurate coordination of the rotary positions of the vanes during operation. For example, the flat parallel sides of the seat and mounting hole are typically sized with a line-to-line clearance which is nominally a zero clearance plus or minus a suitable manufacturing tolerance. Statistically, this means that some levers will have a positive clearance around their seats and are readily seated thereon, and some levers will have a negative clearance around their seats which requires a corresponding assembly force resulting in a tight interference fit with their seats.
The interference fit is typically effected by simply threadingly engaging the retaining nut atop the threaded stem and torquing the nut sufficiently to drive the lever downwardly around its seat in an interference fit therewith. This, however, presents the problem of plastically damaging either the lever or its seat in the event of misalignment therebetween.
Since the mounting hole of a lever in the interference fit example cannot initially engage its corresponding seat, when the nut is initially threaded atop the exposed portion of the stem it hides from view the D-shaped interface between the mounting hole and its seat. If the lever is misaligned atop its seat and the nut is nevertheless torqued into engagement, undesirable plastic deformation around the mounting hole or seat, or both, can occur requiring replacement of either or both components.
Accordingly, it is desired to provide an improved variable stator vane which prevents mismatch assembly between the lever atop its mounting seat.